1. Technical Field
The present invention relates to an improved storage device and in particular to an improved method and system for compensating a head positioning servo within a storage device. Still more particularly, the present invention relates to an improved method and system for maintaining the stability of a head positioning servo utilized with a storage device having multiple heads and reducing the variation of the head positioning servo stability from one head to another head, such that a head for writing to and reading from a storage media device accurately follows a target position of the storage media device surface.
2. Description of the Related Art
One method for compensating head positioning servo is, for example, disclosed in Japanese Patent Kokai Publication No. 09-180388 (hereafter referred to as document A). The method disclosed in document A involves compensation of a position detecting signal or positioning error signal(PES). PES is a signal indicating a head position on a disk surface and consists of a main position detecting signal identified as a main positioning error signal(MPES) and a slave position detecting signal identified as a slave positioning error signal (SPES). A burst pattern formed on the disk surface is read by the head, and a MPES and a SPES are generated according to the read signal and a position detecting signal gain H. The disk surface is partitioned into multiple tracks. The MPES is utilized when the PES is in a certain range of positions in the multiple tracks while the SPES is utilized when the PES is in a remaining range of positions in the multiple tracks.
The method disclosed in document A further includes a step for compensating the position detecting signal gain H of each head in the disk apparatus having multiple disk surfaces and multiple heads corresponding to the individual disk surfaces, so that the MPES and the SPES make a good continuous linkage irrespective of the head to be controlled.
By a second method for compensating head positioning servo, the open-loop gain of the servo (i.e., servo loop gain) is measured for each head, and, if there is a difference between the measured open-loop gain and the design value, a drive control signal gain K, utilized for a drive control signal, is compensated in order to attain stable operation of the servo. The drive control signal is a signal for controlling a driver which moves the head and is generated so as to have a value, according to the PES, that is the difference between the head position and the target position, and the drive control signal gain K.
The PES compensation method described in document A may cause a decrease in the inclination of the PES (referred to as dullness) around the linkage of the MPES and the SPES. For instance, the PES may become dull as depicted by a dotted line (B) in FIG. 8 while a standard PES should be as shown as a solid line (A) in FIG. 8. If the PES becomes dull, the inclination of the PES increases in the transverse center of the track. The traverse center is indicated as the physical position 0 in FIG. 8. This inclination of the PES makes the open-loop gain of the head positioning servo too high and makes the servo operation unstable, which may result in frequent data write errors. To avoid this problem, a second prior art method, which measures the open-loop gain and compensates the drive control signal gain K according to the measured open-loop gain, has been utilized.
However, the second prior art method for compensating the drive control signal gain K as described above does not directly compensate the PES gain H, which corresponds to the inclination of the PES. Therefore, the variability of the PES is high with respect to the amount of physical travel of the head. In particular, the variability of the PES is high with respect to the amount of physical travel of the head in the transverse center of the track, which corresponds to the center of the MPES. Further, the variability of the PES is high on the boundary of the track, which corresponds to the center of the SPES. Moreover, the inclination of the PES varies from head to head. If the inclination of the PES is too large in the track center or varies by head, as described above, it is not ensured that the head follows an exact target position (data write position or read position) in a track.
In view of the aforementioned, it is desirable to provide improved compensation for head positioning servo which causes a head for writing to or reading from a disk to accurately follow a target position on the disk surface. Further, it is desirable to provide improved stability of the compensated head positioning servo for each head and between multiple heads.
In view of the foregoing, it is therefore an object of the present invention to provide an improved storage device.
It is another object of the present invention to provide an improved method and system for compensating a head positioning servo within a storage device.
It is yet another object of the present invention to provide an improved method and system for maintaining the stability of a head positioning servo utilized with a storage device having multiple heads and reducing the variation of the head positioning servo stability from one head to another head, such that a head for writing to and reading from a storage media device accurately follows a target position of the storage media device surface.
In accordance with the method and apparatus of the present invention, an open-loop gain of a head positioning servo is calculated when the head positioning servo causes a head to follow a predetermined position of a target track of a storage media surface by generating a position detecting signal utilizing a position detecting signal gain. A compensated position detecting signal gain is generated by compensating the position detecting signal gain according to a difference between a first predetermined value and the open-loop gain of the head positioning servo, such that variability of the position detecting signal and the open-loop gain is reduced to achieve stability in a head positioning servo.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.